It is known to weld sheets made of non-conductive polar substances by dielectric heating in a high frequency electric field. Plastics such as polyvinyl chloride are ideal for this purpose.
Such sheets can be used as coverings for padded materials, such as for a sun visor used in automobiles. Other similar coverings in sheet form can be fabricated by this process, such as automotive vehicle ceiling liners, head rests, vehicle door paneling, arm rests, seats, etc.
The advantages of joining materials by a dielectric heating technique are the low cost and dependability provided by this method. It is a rapid and dependable process. In addition, if necessary, weld excess can be torn off directly after welding, and without use of special tools. This produces a clean and smooth weld seam which requires litle, if any, working after the welding.
If it is desired to connect ordinary fiber materials such as fabrics, knitted articles, felt, or the like, by buttjoint high-frequency welding, this cannot be done because these ordinary textiles cannot be welded by this technique. They must first be coated with a polar dielectric weldable material which can be welded by high frequency. Additionally, removal of the weld excess by tearing is not possible for plastic coated materials, since the ordinary fiber material is not heated and softened by the high-frequency welding. Such coated textile materials can, therefore, only be cut around the weld seam or be freed of weld excess by stamping.
In such a case, moreover, a wide weld seam is necessary so that good adherence is achieved between the welded materials. Also, a certain minimum seam width is required where the excess is to be removed by stamping techniques. This wide seam is often unsightly and unattractive, and, if nothing more, it often requires further processing.
This invention features the butt-welding of a textile material using dielectric heating induced by a high frequency electric field. A welded textile article produced with material of this invention has a suitable weld seam that is small and smooth and that is free of protruding fiber ends.
An ordinary web of plastic fibers, even if it can be welded by high frequency and consists, for instance, of PVC fibers, still will not produce a suitable bond in the weld seam, and will produce an unsightly weld seam with protruding fiber ends that require removal by cutting or stamping.
Microscopic examination of the weld seams of previously fabricated textile articles, like woven and knitted fabrics, felts and non-wovens, have revealed that the unsightly seams were caused by insufficient weldable plastic material in the region of the welding electrode. The lack of the plastic produced a bond in which many of the threads or fibers were not welded to each other, causing a weak weld seam having protruding fibers. The weld excess or residue is manually torn off immediately following welding. But, only a fraction of the fibers present in the material are welded to each other. The greater part of the fibers are separated and have their ends free in the region of the weld seam. They, therefore, do not contribute to the strength of the weld seam. Also, the protrusion of their ends out of the weld seam produces an unattractive appearance.